Aqueous coating agent, preparation of the same and use thereof for multi-layered lacquering

ABSTRACT

Aqueous coating agents suitable for multi-layered finishes containing an aqueous binder dispersion based on polyurethane/polymer hybrid polymers with a ratio by weight of polyurethane fraction to polymer fraction of 0.1:1 to 50:1, with a hydroxyl value of 0 to 150 mg KOH/g, an acid value of 1.5 to 60 mg KOH/g, and a concentration of 0.5 to 300 mmol of silicon per 100 g of solid resin in the form of siloxane bridges (—Si—O—Si—) incorporated into the polyurethane fraction and/or in the form of silanol groups bonded to the polyurethane fraction, obtainable by polymerization of olefinically unsaturated monomers in the presence of polyurethane prepolymers which do not contain olefinic double bonds.

BACKGROUND OF THE INVENTION

The invention provides aqueous coating agents which contain aqueousbinder dispersions based on hybrid polymers which are prepared byradical copolymerisation of olefinically unsaturated monomers in thepresence of aqueous dispersed polyurethane resins which contain siloxanebridges and/or silanol groups but do not contain double bonds. It alsoprovides a process for preparing the aqueous coating agents and aprocess for multi-layer finishing using these coating agents, inparticular as a water-based base-coat lacquer in a process for preparingdecorative multi-layer finishes of the water-based base-coatlacquer/clear lacquer type.

Polyurethane/poly(meth)acrylate hybrid polymers are known as binders foraqueous coating agents.

EP-A-0 297 576 describes the polymerisation of (meth)acrylic monomers inthe presence of previously prepared polyurethane dispersions. After thecompletion of polymerisation, aqueous base-coat lacquers can be preparedfrom the dispersions obtained.

EP-A-0 353 797 describes the preparation of a hydroxy-functionalpolyurethane resin in an olefinically unsaturated monomer as solvent,wherein the unsaturated monomer may be reactive towards isocyanate.After converting the polyurethane solution into the aqueous phase,emulsion polymerisation is performed. The hybrid polymer dispersionobtained may be used as a water-based base-coat lacquer binder.

WO 95 28 429 discloses aqueous polyurethane dispersions suitable for useas binders for water-based base-coat lacquers which are stabilised byionic and/or hydrophilic groups and are based on polyurethane resinschain-lengthened via siloxane bridges.

WO 95 28 428 discloses a process for preparing a multi-layered finish byusing a self-cross-linking water-based base-coat lacquer which contains,as binder, an aqueous polyurethane resin dispersion based on apolyurethane resin with hydroxyl groups and/or R′O groups which arebonded to silicon in lateral and/or terminal positions.

In order to avoid the appearance of sagging, it is desirable thataqueous coating agents have high run limits. Otherwise, the layers canbe applied in only limited thicknesses and, in particular in the case ofcolours with low covering power, application in several spray passeswith intermediate drying, or intermediate evaporation is required.

The applicant suggested, in patent applications PCT/EP 97/04821 and P197 46 327 which do not have priority over this document, coating agentswhich can be used as water-based base-coat lacquers which containaqueous binder dispersions based on hybrid polymers which are preparedby the radical copolymerisation of polyurethane resins which containsiloxane bridges and/or silanol groups and also olefinic double bondswith olefinically unsaturated comonomers.

The object of the present invention is the provision of aqueous coatingagents with high sagging limits which are suitable in particular formulti-layered finishes, in particular for the provision of colour and/oreffect-providing layers. They are intended to be applicable in only asingle spray pass in a thick layer to give an opaque surface coating.

SUMMARY OF THE INVENTION

The invention provides aqueous coating agents containing an aqueousbinder dispersion and also optionally one or more organic solvents,cross-linking agents, pigments, fillers, conventional lacquer additivesand/or one or more further binders, which are characterised in that theaqueous binder dispersion is based on polyurethane/polymer hybridpolymers with a ratio by weight of polyurethane fraction to polymerfraction of 0.1:1 to 50:1, wherein the polyurethane fraction of thepolyurethane/polymer hybrid polymer does not contain any olefinic doublebonds and has a hydroxyl value of 0 to 150, with respect to the solidresin, wherein hydroxyl groups bonded to silicon do not enter into thecalculation for the OH value, and an acid value of 1.5 to 60 mg KOH/g,with respect to solid resin, and a concentration of 0.5 to 300 mmol ofsilicon per 100 g of solid resin in the form of siloxane bridges(—Si—O—Si—) incorporated into the polyurethane fraction and/or in theform of silanol groups bonded to the polyurethane fraction. Thepolyurethane/polymer hybrid polymers are obtainable by polymerisation ofolefinically unsaturated monomers in the presence of polyurethaneprepolymers which do not contain olefinic double bonds.

The hybrid polymers consist of polyurethane fractions and polymerfractions. The polyurethane fraction and the polymer fraction may bepresent as an interpenetrating network and/or the polymer fraction maybe grafted onto the polyurethane fraction. The olefinic double bonds inthe olefinically unsaturated monomers which participate in building upthe polymer fraction in the polyurethane/polymer hybrid polymer areallylic and/or vinylic double bonds and/or alpha/beta-unsaturatedcarbonyl groups, for example preferably (meth)acrylic double bonds. Theproportion of allylic double bonds is preferably less than 10%, whereasthe proportion of (meth)acryloyl groups is at least 50%, preferably morethan 70%. If more than 50% of the olefinic double bonds contributing topolymerisation are from (meth)acryloyl groups, then the hybrid polymersare polyurethane/poly(meth)acrylate hybrid polymers.

DETAILED DESCRIPTION OF THE INVENTION

The binder dispersion based on polyurethane/polymer hybrid polymers usedin aqueous coating agents according to the invention has an acid valueof 1.5 to 60 mg KOH/g, preferably 3 to 40 mg KOH/g, with respect tosolid resin. At least 70% of the acid groups are preferably exclusivelyconstituents of the polyurethane fraction. The acid groups stabilise thehybrid polymer particles in the aqueous phase. The polyurethane/polymerhybrid polymers may contain additional stabilising hydrophilic non-ionicgroups, for example polyalkylene oxide groups, e.g. polyethylene oxidegroups.

The binder dispersion based on polyurethane/polymer hybrid polymers usedin aqueous coating agents according to the invention have a hydroxylvalue of 0 to 150, preferably less than 100 mg KOH/g, with respect tosolid resin. The optional hydroxyl value of the binder may arise fromthe polyurethane fraction and/or from the polymer fraction.

The aqueous binder dispersions which can be used in aqueous coatingagents according to the invention are based on hybrid polymers which canbe prepared by radical polymerisation of olefinically unsaturatedmonomers in the presence of polyurethane resins which contain siloxanebridges and/or silanol groups but which do not contain olefinic doublebonds.

The aqueous binder dispersions based on polyurethane/polymer hybridpolymers can be prepared, for example, by converting a polyurethaneprepolymer which contains acid groups and does not contain olefinicdouble bonds, which has, on average, 0.7 to 9 R′—O groups bonded tosilicon per molecule, in which

R′=C1 to C8 alkyl or C(O)R′″, and

R′″=C1 to C10 alkyl

and which may be present dissolved in a solvent which is inert towardsisocyanate, optionally after previous neutralisation of the acid groups,into an aqueous dispersion by adding water, and then subjecting theprepolymer, together with olefinically unsaturated monomers, to radicalpolymerisation. The olefinically unsaturated monomers may be addedbefore and/or after preparation of the aqueous dispersion. For example,the olefinically unsaturated monomers, or some of them, may take on thefunction of a solvent which is inert towards isocyanate prior topreparing the aqueous dispersion, and these do not have to be removed ata later stage.

Polyurethane prepolymers which contain acid groups but do not containolefinic double bonds and with, on average, 0.7 to 9, preferably lateraland/or terminal silicon-bonded R′O groups per molecule may be prepared,for example, by preparing a linear or branched, non-gelled, polyurethaneprepolymer which does not contain olefinic double bonds but does containacid groups and is hydroxy-functional in an inert organic solvent(mixture) and/or in one or more olefinically unsaturated monomers,present as a mixture, which are inert towards isocyanate or in theabsence of solvents and olefinically unsaturated monomers and reactingthe hydroxyl groups in the polyurethane prepolymer obtained in this waywith one or more silanes of the general formula

((OCN—)_(n)R)_(a)Si(OR′)_(b)(R″)_(c)

where R=a bifunctional, trifunctional or tetrafunctional, preferablybifunctional, organic group with a molecular weight of 13 to 500,preferably (ar)alkylene with 1 to 12 carbon atoms, particularlypreferably alkylene with 1 to 12 carbon atoms, R′=C1 to C8 alkyl orC(O)R′″, preferably C1 to C4 alkyl, R″=R′″=C1 to C10 alkyl, wherein R″and R′″ may be identical or different, a=1, 2 or 3, preferably 1, b=1, 2or 3, preferably 2 or 3, c=0, 1 or 2, n=1 to 3, preferably 1 or 2,particularly preferably 1, wherein several groups R′, R″ and R′″ areidentical or different and in which the sum of a plus b plus c is four.

The polyurethane prepolymers which contain acid groups but do notcontain olefinic double bonds and with on average 0.7 to 9 preferablylateral and/or terminal silicon-bonded R′O groups per molecule arepreferably prepared, for example, by:

1) preparing a linear or branched, non-gelled, polyurethane prepolymerwhich does not contain olefinic double bonds but does contain acidgroups and is also isocyanate-functional in an inert organic solvent(mixture) and/or in one or more olefinically unsaturated monomers,present as a mixture, which are inert towards isocyanate or in theabsence of solvents and olefinically unsaturated monomers,

2) reacting the free isocyanate groups in the polyurethane prepolymerobtained in this way

a1) with one or more compounds of the general formula

((H—X—)_(n)R)_(a)Si(OR′)_(b)(R″)_(c)  (I)

where X═O, S, NH or NR′^(v), preferably NH or NR′^(v), R=a bifunctional,trifunctional or tetrafunctional, preferably bifunctional, organic groupwith a molecular weight of 13 to 500, preferably (ar)alkylene with 1 to12 carbon atoms, particularly preferably alkylene with 1 to 12 carbonatoms, R′=C1 to C8 alkyl or C(O)R′″, preferably C1 to C4 alkyl,R″=R′″=C1 to C10 alkyl, wherein R″ and R′″ may be identical ordifferent, R′^(v)=C1 to C8 alkyl, a=1, 2 or 3, preferably 1, b=1, 2 or3, preferably 2 or 3, c=0, 1 or 2, n=1 to 3, preferably 1 or 2,particularly preferably 1, wherein several groups R′, R″ and R′″ areidentical or different and in which the sum of a plus b plus c is four,

a2) optionally with alkanolamines which contain one or more NH, and/orNH groups and have an OH-functionality of at least 1, and

a3) optionally with one or more aliphatic C4-C36 alcohols and/or amines.

The preparation of R′OSi-functionalised polyurethane prepolymers viaNCO-prepolymers may be performed in a so-called one-stage process, i.e.the previously described process steps 1) and 2) may be performedsimultaneously by reacting together the reactants required there all atthe same time or preferably in a sequential method of preparation. Whenchoosing the reaction partners, the reaction conditions and the sequenceof addition of the individual reaction partners, care should be taken toensure that undesired secondary reactions are excluded.

Preparation of the linear or branched, non-gelled, polyurethaneprepolymers which do not contain olefinic double bonds but do containacid groups and are also isocyanate-functional, taking place for examplein step 1), may be performed, for example, by reacting one or morecompounds with at least two groups which can react with isocyanate, inparticular one or more polyols, preferably diols, with one or moreorganic polyisocyanates, preferably diisocyanates and with one or morecompounds with more than one, preferably two, groups which can reactwith isocyanate groups and at least one acid group.

For example, a NCO group-containing polyurethane prepolymer which can beused as a starting product can be prepared by reacting, in an anhydrousmedium,

b1) at least one linear or branched compound which contains at least twogroups which can react with isocyanate and with an average molecularweight of 60-10,000, preferably 60-6000,

b2) at least one organic polyisocyanate, in particular a diisocyanate,

b3) at least one compound with more than one group which can react withisocyanate, and at least one acid group, with a number average molecularweight (Mn) of up to 10,000, preferably up to 2000 with a NCO/OH ratioof more than 1 to 4:1.

The previously mentioned linear or branched compound in component b1) ispreferably at least one polyol based on one or more polyethers,polyesters and/or polycarbonates, with at least two OH groups in themolecule and a number average molecular weight (Mn) of 600-10,000,preferably more than 1000 and less than 6000, optionally also using oneor more at least difunctional low molecular weight alcohols and/oramines and/or aminoalcohols with a molecular weight of less than 600,preferably less than 400.

All the methods of preparation of NCO group-containing polyurethaneprepolymers may be performed as single-stage or multi-stage processes.

The isocyanate group-containing polyurethane prepolymers have aconcentration of urethane (—NHCOO—) and optionally urea (—NHCONH—)groups of preferably between 10 and 300 milliequivalents per 100 g ofsolid resin.

The compounds used as component b1) to prepare NCO group-containingpolyurethane prepolymers may be, for example, a linear or branchedpolyol component, e.g. diols. They are, for example, polyols which areused in the field of polyurethane chemistry and are familiar to a personskilled in the art. If the starting compound is a linear diol, aproportion of polyols with a functionality of 3 or more may be used toproduce branching of the polymer. Here, the amount has to be chosen insuch a way that no gel formation takes place during synthesis of the NCOgroup-containing polyurethane prepolymers.

Examples of polyol component b1) may be polyetherpolyols, in particularpolyetherdiols, for example polyethylene glycols, polypropylene glycolsor polytetrahydrofurandiols.

Polyesterpolyols may be mentioned as further examples of polyolcomponents b1). The polyester polyols may be prepared, for example, byesterification of organic dicarboxylic acids or their anhydrides withorganic polyols. The dicarboxylic acids and polyols may be aliphatic,cycloaliphatic or aromatic dicarboxylic acids and polyols. The polyesterpreferably has a molecular weight of 300 to 6000, an OH value of 20 to400 and an acid value of less than 3, preferably less than 1. Linearpolyesters, that is polyesterdiols, are preferably used.

Polycarbonatediols, for example, may also be used as component b1).

Furthermore, polyesterpolyols, preferably polyesterdiols, which arederived from lactones, can also be used as component b1).

The low molecular weight compounds optionally also used in b1) are inparticular alcohols and amines. They are at least difunctional compoundswhich contain hydroxyl and/or amine groups, have a molecular weight ofless than 600, preferably less than 400, and are known per se frompolyurethane chemistry in the context of an isocyanate additionreaction. Either difunctional compounds or at least trifunctionalcompounds, or any mixture of these types of compounds, are suitable inthe context of the isocyanate addition reaction.

Any organic polyisocyanates such as, for example, diisocyanates, may beused as component b2). Aliphatic, cycloaliphatic, aromatic oraraliphatic diisocyanates my be used. Examples of suitable diisocyanatesare hexamethylene diisocyanate, isophorone diisocyanate,bis-(4-isocyanatocyclohexyl)-methane, bis-(4-isocyanatophenyl)-methane,tetramethylxylylene diisocyanate and 1,4-cyclohexylene diisocyanate.

As component b3), low molecular weight compounds which contain more thanone, preferably two or at least two, groups which react with isocyanateand at least one acid group are preferably used. Suitable groups whichreact with isocyanate are in particular hydroxyl groups and primary andsecondary amine groups. Carboxyl, phosphoric acid and sulfonic acidgroups, for example, are suitable as acid groups. The acid groupspreferably incorporated are carboxyl groups; they may be introduced, forexample, by using hydroxyalkanecarboxylic acids as component b3).

Dihydroxyalkanoic acids are preferred, in particularalpha,alpha-dimethylolalkanoic acids such asalpha,alpha-dimethylolpropionic acid.

Acid polyesters such as are described in DE-A-39 03 804 may also be usedas component b3).

The amounts of b1), b2) and b3) are chosen so that the reaction producesa reaction product with lateral and/or terminal NCO groups, i.e. anexcess of polyisocyanate is used. An NCO to OH ratio of more than 1 to4:1 may be used, but this ratio is preferably in the range 1.1 to 2:1,particularly preferably 1.1 to 1.7:1. The reaction product may have abranched structure, but a linear structure with terminal NCO groups isgenerally preferred.

The NCO group-containing polyurethane prepolymer obtained in processstep 1) is reacted in process step 2)

a1) with one or more compounds of the general formula

((H—X—)_(n)R)_(a)Si(OR′)_(b)(R″)_(c)  (I)

where X═O, S, NH or NR′^(v), preferably NH or NR′^(v), R=a bifunctionalto tetrafunctional, preferably bifunctional, organic group with amolecular weight of 13 to 500, preferably (ar)alkylene with 1 to 12carbon atoms, particularly preferably alkylene with 1 to 12 carbonatoms, R′=C1 to C8 alkyl or C(O)R′″, preferably C1 to C4 alkyl,R″=R′″=C1 to C10 alkyl, R′^(v)=C1 to C8 alkyl, a=1, 2 or 3, preferably1, b=1, 2 or 3, preferably 2 or 3, c=0, 1 or 2, n=1 to 3, preferably Ior 2, particularly preferably 1 and in which the sum of a plus b plus cis four,

a2) optionally with alkanolamines which contain one or more NH₂ and/orNH groups and have an OH-functionality of at least 1, and

a3) optionally with one or more aliphatic C4-C36 alcohols and/or amines,

to give a R′OSi-functionalised polyurethane prepolymer which containsacid groups and does not contain olefinic double bonds.

Compounds of the general formula (I) are silane derivatives whichcontain groups of the (H—X—)_(n)R— type with active hydrogen atoms whichcan react with isocyanate groups to give an addition product. The activehydrogen-containing, functional HX-groups are preferably amine groups, nhas a value from 1 to 3, n preferably has the value 1. The group R is abifunctional to tetrafunctional, preferably bifunctional group, whichmay contain chemically inert groups or substituents, with a molecularweight of 13 to 500. Group R is preferably a bifunctional (ar)alkylenegroup with 1 to 12 carbon atoms. An alkylene group with 1 to 12 carbonatoms is particularly preferred as group R.

Furthermore, the silane derivative of the general formula (I) contains 1to 3, preferably 2 or 3 R′—O groups bonded to silicon, wherein R′preferably represents a C1 to C8 alkyl group.

A few preferred examples of compounds (I) which may be mentioned arebeta-aminoethyltriethoxysilane, gamma-aminopropyltriethoxysilane,gamma-aminopropyltrimethoxysilane, gamma-aminopropylethyldiethoxysilane,gamma-aminopropyl-phenyldiethoxysilane,gamma-aminopropyltrimethoxysilane, delta-aminobutyltriethoxy-silane,delta-aminobutylethyldiethoxysilane,N-(2-aminoethyl)-3-aminopropyl)-trimethoxysilane,N-2-aminoethyl-3-aminopropyl-tris(2-ethylhexoxy)silane,6-(amino-hexylaminopropyl)trimethoxysilane,N-aminoethyl-3-aminopropylmethyldimethoxy-silane.

Reaction of the NCO-functional polyurethane prepolymers to giveR′OSi-functionalised polyurethane prepolymers takes place with completeconsumption of the HX groups in compounds (I).

The polyurethane/polymer hybrid polymers which are used to produce thebinder dispersion to be used in aqueous coating agents according to theinvention may contain hydroxyl groups. If this is required, then the NCOgroup-containing polyurethane prepolymers are reacted with at least oneNH₂ and/or NH group-containing alkanolamine with an OH functionality ofat least 1, in the context of optional process step a2), duringpreparation of the R′OSi-functionalised polyurethane prepolymer. Thereaction then takes place with complete consumption of the NH, and/or NHgroups in the alkanolamine.

Alkanolamines which contain NH₂ and/or NH groups and have an OHfunctionality of at least 1 are compounds which may be used as thesupplier of the hydroxyl groups in the binder dispersion and contribute,solely or together with any hydroxyl groups from the polymer fraction,to the hydroxyl value of the binder. The NH or NH₂ groups in thealkanolamines have a much higher reactivity towards the isocyanategroups in the NCO-functional PU prepolymers than that of the OH groups,i.e. the NH groups react preferentially with the isocyanate groups toform a urea.

Examples of suitable alkanolamines with an OH functionality of at least1 are monoalkanolamines and dialkanolamines, e.g. diethanolamine,N-methylethanolamine, diisopropanolamine, N-ethylispropanolamine,monoisopropanolamine, ethanolamine, 2,2-aminoethoxyethanol,monoethylethanolamine, butylethanolamine, cyclohexyl-ethanolamine,3-aminopropanol, 2-aminobutanol-1.

It may be expedient also to use one or more aliphatic C4-C36 alcoholsand/or amines, reaction of which generally takes place with completeconsumption of their OH, NH and/or NH₂ groups, in optional process stepa3), instead of or together with the NH, and/or NH group-containingalkanolamines. Fatty amines and/or fatty alcohols with more than 12carbon atoms are preferred. Examples are lauryl alcohol, stearyl alcoholand the corresponding amines.

The isocyanate groups in the NCO-functional polyurethane prepolymers arepreferably reacted with the HX groups from (I), the NH groups in theoptionally used alkanolamine and the groups which can react withisocyanate in the optionally used C4-C36 alcohol and/or amine in thestoichiometric ratio. The alkanolamine, C4-C36 alcohol and/or amine andcompound (I) may be reacted with the NCO-functional polyurethaneprepolymer as a mixture or one after the other in a suitable sequence.

Any optionally still remaining residual free isocyanate groups in thepolyurethane prepolymers with on average 0.7 to 9 R′O groups bonded tosilicon per molecule may be reacted with conventional compounds whichcontain active hydrogen atoms capable of adding onto isocyanate beforeconversion of the prepolymers into the aqueous phase. Examples ofsuitable active hydrogen-containing compounds are monoalcohols, diols,polyols, glycol ethers, monoamines, diamines, polyamines.

Reaction of the components used to build up the NCO-functionalpolyurethane prepolymers and also further reaction to giveR′OSi-functionalised polyurethane prepolymers takes place in ananhydrous medium, for example at temperatures of 20 to 140° C.,preferably between 50 and 100° C. The process may be solvent-free or, asis familiar per se to a person skilled in the art, may be performed inorganic solvents suitable for polyurethane synthesis. Water-misciblesolvents or water-immiscible solvents may be used as solvents. Ingeneral it is advantageous to use those solvents which can be removed atany stage of the preparation of aqueous binder systems (for example,after they have been finally prepared), for example by distilling off,optionally under reduced pressure.

Examples of suitable solvents are ketones, e.g. acetone, methyl ethylketone, methyl isobutyl ketone; N-alkylpyrrolidones such as e.g.N-methylpyrrolidone; ethers such as e.g. diethylene glycol dimethylether, dipropylene glycol dimethyl ether, or also cyclic ureaderivatives such as 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone.

The polyurethane prepolymer with on average 0.7 to 9 R′OSi groups bondedto silicon per molecule obtained in this way is converted into anaqueous dispersion by adding water, preferably after neutralising theacids groups. All or some of the acid groups may be converted into thecorresponding salt groups with a neutralising agent. This may take placein all stages of the previously described synthesis, wherein it shouldbe noted that the choice of compounds used for salt production is madein such a way that these behave in a chemically inert manner during thesynthesis.

Bases are used for the neutralisation process, e.g. amines, preferablytertiary amines. Examples of suitable bases are ammonia or organicamines such as 2-amino-2-methylpropanol-1; trialkylamines such astrimethylamine, triethylamine, triisopropylamine; N-alkylmorpholinessuch as N-methylmorpholine; N-dialkyl-alkanolamines such asN-dimethylethanolamine and N-dimethylisopropanolamine and mixtures ofthese.

Conversion into an aqueous dispersion may take place in such a way thatthe polyurethane prepolymer is mixed with water. For this purpose, theentire amount of water in one portion or, preferably, only some of thetotal amount of water is mixed with the polyurethane prepolymer. Thewater may be added to the resin. It is also possible to add the resin tothe water.

The R′OSi groups in the polyurethane prepolymer are sensitive tohydrolysis. A variety of products may be obtained during the course ofadding water. For example, it is possible to control whether the hybridbinder contains silicon in the form of siloxane bridges (—Si—O—Si—)incorporated in the polyurethane fraction or in the form of silanolgroups bonded to the polyurethane fraction and also the ratio ofsiloxane bridges to silanol groups.

If the hybrid polymer is intended to contain silicon in the form ofsilanol groups, for example substantially only in the form of silanolgroups, then it is essential that an amount of water is added, within ashort time, which is sufficient to prevent further reaction of thesilanol groups formed by hydrolysis. The addition of water takes placeusing more than ten times the stoichiometric excess over the amount ofwater required to hydrolyse the R′OSi groups. At least 50 times thestoichiometric excess is preferably added. The addition of water isparticularly preferably performed in such a way that at least half ofthe amount of water required to prepare the aqueous dispersion is addedin one portion. Any condensation of the silanol groups formed byhydrolysis to give siloxane bridges, with the elimination of water, islargely avoided by adding sufficient water, i.e. an aqueous dispersionof a polyurethane resin which contains virtually no siloxane bridges andwhich contains silanol groups is obtained.

Preferably, however, the polyurethane prepolymer is subjected to achain-lengthening procedure with the formation of siloxane bridges byadding a small amount of water which is not sufficient to convert themixture into the aqueous phase, for example, preferably at least thestoichiometric amount to hydrolyse the R′OSi groups and converting thereaction product into an aqueous dispersion during or after thechain-lengthening procedure, optionally after complete or partialneutralisation. Chain-lengthening of the R′OSi-functionalisedpolyurethane prepolymer takes place after adding a preferably up to atmost ten times the stoichiometric excess, particularly preferably up toat most five times the stoichiometric excess, the calculation beingbased on the amount of water required to hydrolyse the R′OSi groups.Hydrolysis of the R′OSi groups takes place rapidly. The silanol groupsformed by hydrolysis condense with the elimination of water to givesiloxane bridges and thus lead to a chain-lengthened polyurethane resinwhich is virtually free of silanol groups, for example more than 80%, inparticular more than 90%, of the silicon is present bonded as siloxanebridges. Depending on the R′OSi-functionalised polyurethane prepolymerused, linear, branched or cross-linked products may be obtained.

Converting the optionally neutralised reaction product into an aqueousdispersion by adding a sufficient amount of water may take place duringor after chain-lengthening and formation of the siloxane bridges takesplace in the dispersed or non-dispersed resin phase, i.e.chain-lengthening proceeds in the resin phase; thus, if the resin hasalready been dispersed by adding a sufficient amount of water, thenchain-lengthening takes place in the dispersion particles themselves.

The hydrolysis reaction and the optionally proceeding chain-lengtheningprocess also occurring may, if desired, be performed at elevatedtemperature. Temperatures of up to 95° C., for example, are suitable.

Preparing the aqueous dispersion of the polyurethane resin whichcontains siloxane bridges and/or silanol groups may be performed byknown processes. For example, it is possible to initially introduce theneutralised resin and to add the water while thoroughly dispersing.Likewise, the water phase, optionally containing the neutralising agent,may be initially introduced and the resin is then incorporated withstirring. A continuous method of working is also possible, i.e. resin,water and neutralising agent are simultaneously homogeneously mixedtogether in known units, e.g. a rotor-stator mixer. Conversion into theaqueous phase may be promoted by an elevated temperature.

The polyurethane resin, present in a solvent-free form or in an organicsolution, is converted into the aqueous phase by adding a sufficientamount of water. Addition of the amount of water sufficient to convertinto the aqueous phase may take place after completing thechain-lengthening process. It is also possible to add the majority ofthe water during chain-lengthening and after hydrolysis of the R′OSigroups. A finely divided polyurethane dispersion with an averageparticle size of greater than 10 and less than 2000 nm, preferablygreater than 50 and less than 500 nm, is produced. The distribution maybe monomodal or bimodal, preferably monomodal.

After producing the aqueous dispersion of polyurethane resin whichcontains siloxane bridges and/or silanol groups, preferablysubstantially only siloxane bridges, the last synthesis stage forpreparation of the binder dispersion is performed. This is building upthe polymer fraction in the polyurethane/polymer hybrid polymer binderby radical polymerisation using methods which are known per se. Radicalpolymerisation may be a copolymerisation, proceeding in the presence ofthe aqueous dispersed polyurethane resin which contains siloxane bridgesand/or silanol groups and does not contain olefinic double bonds, of theolefinically unsaturated monomers used to build up the polymer fractionof the polyurethane/polymer hybrid polymer binder, or it may be a graftpolymerisation of the olefinically unsaturated monomers used to build upthe polymer fraction of the polyurethane/polymer hybrid polymer binderon the polyurethane fraction of the polyurethane/polymer hybrid polymerbinder, initiated by H-abstraction from the aqueous dispersedpolyurethane resin which contains siloxane bridges and/or silanol groupsand does not contain olefinic double bonds, or both forms of radicalpolymerisation may proceed in parallel. If polyunsaturated monomers arealso used during radical polymerisation of the olefinically unsaturatedmonomers, then radical polymerisation may take place in such a way thatthe polyunsaturated monomers are copolymerised with complete consumptionof their olefinic double bonds or so that some of the polyunsaturatedmonomers are copolymerised with incomplete consumption of their olefinicdouble bonds. For example, some of the polyunsaturated monomers may becopolymerised using only some of the relevant unsaturated groups so thatthe polymer fraction in the resulting polyurethane/polymer hybridpolymers may still contain olefinic double bonds.

The olefinic double bonds participating in the polymerisation processare allylic and/or vinylic double bonds and/or alpha,beta-unsaturatedcarbonyl groups, for example preferably (meth)acrylic double bonds. Theproportion of allylic double bonds is preferably less than 10%, whereaspreferably at least 50%, preferably more than 70% of the double bondsare from (meth)acryloyl groups.

Some or all of the olefinically unsaturated monomers may already bepresent in the aqueous dispersion, as explained above when describingtheir function as solvent during synthesis of the polyurethane resin or,preferably, at least some of them are added and polymerised afterproducing the aqueous dispersion. Olefinically unsaturated monomers andradical initiators may be added together, for example as a mixture ordissolved one in the other, or separately, for example also added atdifferent times. It may be expedient to perform the addition of monomersand initiator in such a way that no changes in the solids content areproduced during radical polymerisation.

Radical polymerisation is performed at temperatures between 20 and 95°C., preferably between 60 and 90° C.

Examples of radical initiators, which may be used in conventionalamounts, are peroxide compounds such as dialkyl peroxides, diacylperoxides, organic hydroperoxides, peresters, ketone peroxides; azocompounds such as azoisobutyronitrile. Water-soluble radical initiatorssuch as, for example, hydrogen peroxide, ammonium peroxydisulfate,ammonium persulfate, ammonium salts of 4,4′-azobis(4′-cyanopentanoicacid),2,2′-azobis(2-methyl-N-1,1-bis(hydroxymethyl)-ethyl)-propionamide,2,2′-azobis(2-methyl-N-2-hydroxyethyl)propionamide.

It is also possible to perform the polymerisation as a redoxpolymerisation by using corresponding redox initiator systems such as,for example, sodium sulfite, sodium dithionite, ascorbic acid andperoxide compounds.

Radically polymerisable, olefinically unsaturated monomers which may beused are those monomers which do not contain functional groups. Examplesare monovinyl aromatic compounds, preferably with 8 to 10 carbon atomsper molecule, such as styrene, vinyltoluene; vinylethers and vinylesters such as vinyl acetate, vinyl versatate; dialkyl maleates,fumarates, tetrahydrophthalates, but in particular (cyclo)alkyl(meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate,propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate,cyclohexyl (meth)acrylate, ethylhexyl (meth)acrylate, dodecyl(meth)acrylate, lauryl (meth)acrylate, isobornyl (meth)acrylate.

In addition to the non-functional monomers, olefinically unsaturatedmonomers with functional groups may also be used. Examples are thosewith CH-acidic, epoxide, hydroxyl or carboxyl groups, wherein it shouldbe noted that the carboxyl-functional monomers should contribute notmore than 30% of the acid value of the polyurethane/polymer hybridpolymer binder.

Examples of olefinically unsaturated monomers with hydroxyl groups,which may contribute to the hydroxyl value of the binder according tothe invention, solely or together with any hydroxyl groups in thepolyurethane fraction, are allyl alcohol, but in particular hydroxyalkyl(meth)acrylates such as hydroxyethyl (meth)acrylate, hydroxypropyl(meth)acrylate or butanediol mono(meth)acrylate, glycerolmono(meth)acrylate, adducts of (meth)acrylic acid and monoepoxides suchas e.g. glycidyl esters of versatic acid, adducts of glycidyl(meth)acrylate and monocarboxylic acids such as e.g. acetic acid orpropionic acid.

Examples of carboxyl group-containing olefinically unsaturated monomersare unsaturated carboxylic acids such as e.g. (meth)acrylic, itaconic,crotonic, isocrotonic, aconitic, maleic and fumaric acids, semi-estersof maleic and fumaric acid.

A proportion of olefinically unsaturated monomers with at least twopolymerisable olefinic double bonds may also be used. The proportion ofthese monomers may be, for example, 0 to less than 5 wt. %, with respectto the total weight of monomers used to build up the polymer fraction.The proportion of these monomers may also be higher, however, when, forexample, the polymer fraction is intended to be more highly branched orcross-linked, the proportion may then be, for example, 5 to 45 wt. % ofpolyunsaturated monomers, with respect to the total weight of monomersused to build up the polymer fraction. Polyunsaturated monomers aregenerally exclusively low molecular weight compounds defined by anempirical formula with a molecular weight of generally less than 500.Examples are divinylbenzene, hexanediol di(meth)acrylate, ethylene andpropylene glycol di(meth)acrylate, 1,3- and 1,4-butanedioldi(meth)acrylate, vinyl (meth)acrylate, allyl (meth)acrylate, diallylphthalate, glycerol tri(meth)acrylate and di(meth)acrylate,trimethylolpropane tri(meth)acrylate and di(meth)acrylate,pentaerythritol tri(meth)acrylate and tetra(meth)acrylate, di- andtripropylene glycol di(meth)acrylate.

When preparing the aqueous binder dispersion, the proportions by weightof the individual reactants are preferably chosen in such a way and thereaction is performed in such a way that the polyurethane/polymer hybridpolymer on which the aqueous binder dispersion is based has a ratio byweight of polyurethane fraction to polymer fraction of 0.1:1 to 10:1, ahydroxyl value of 0 to 150, preferably less than 100 mg KOH/g, withrespect to solid resin, wherein hydroxyl groups bonded to silicon arenot taken into account when calculating the OH value, and an acid valueof 1.5 to 60 mg KOH/g, preferably 3 to 40 mg KOH/g, with respect tosolid resin and a concentration of 0.5 to 300 nmol, preferably 1 to 200mmol, particularly preferably 5 to 75 mmol of silicon per 100 g of solidresin in the form of siloxane bridges (Si—O—Si) incorporated in thepolyurethane fraction and/or in the form of silanol groups bonded to thepolyurethane fraction.

The solids content of the binder dispersions used in the aqueous coatingagents according to the invention is preferably between 25 and 65 wt. %,particularly preferably more than 35 and less than 60 wt. %.

Solvents optionally contained in the aqueous binder dispersion may, ifrequired, be removed by distillation. This may take place under reducedpressure, for example before or after radical polymerisation.

Aqueous coating agents according to the invention may be prepared fromthe aqueous binder dispersions. These are preferably water-basedbase-coat lacquers. Aqueous coating agents according to the inventionmay be self-drying (physically drying), self-cross-linking or externallycross-linking. The polyurethane/polymer hybrid polymers on which thebinder dispersions are based have hydroxyl numbers between 0 and 150,preferably between 0 and 100 mg KOH/g. The hydroxyl value is preferablyin the upper part of this range of values if externally cross-linkingaqueous coating agents are intended to be prepared.

To prepare aqueous coating agents, preferably water-based base-coatlacquers, pigments, further binders, additives and optionally smallamounts of solvents, for example, are added to the aqueous binderdispersion.

Aqueous coating agents according to the invention may contain, inaddition to the aqueous binder dispersion, one or more additionalbinders which differ therefrom. Examples of such additional binders arethe conventional film-forming, water-soluble or water-dilutable resinswhich are familiar to a person skilled in the art, such aswater-dilutable polyester resins, water-dilutable polyacrylate resins,water-dilutable polyurethane resins and/or those water-dilutable bindersin which (meth)acrylic copolymers and polyurethane resins or(meth)acrylic copolymers and polyester resin are associated in acovalently bonded form or in the form of interpenetrating resinmolecules. These may be reactive or non-functional resins. The amount ofadded resin may be 0 to 75 wt. %, preferably 0 to 50 wt. %, of the totalresin solids. 0 to 30 wt. % is particularly preferred. In thisconnection, resin solids means the sum of all the binders without across-linking component.

To prepare aqueous coating agents according to the invention, variouscross-linking agents such as, for example, formaldehyde condensationresins, such as phenol/formaldehyde condensation resins andamine/formaldehyde condensation resins, and also free or blockedpolyisocyanates, may be used. The cross-linking agents may be usedindividually or as a mixture. The ratio of mixing of cross-linking agentto binder is preferably 10:90 to 40:60, particularly preferably 20:80 to30:70, each with respect to the weight of solids.

Furthermore, aqueous coating agents according to the invention maycontain polymeric microparticles which are known to a person skilled inthe art. Cross-linked or non-cross-linked microparticles may be used.

Furthermore, aqueous coating agents according to the invention maycontain lacquer additives, for example rheology-regulating agents, suchas highly disperse silica, inorganic layered silicates or polymeric ureacompounds. Compounds which also act as thickeners are, for example,water-soluble cellulose ethers such as hydroxyethyl cellulose, methylcellulose or carboxymethyl cellulose, and also synthetic polymers withionic and/or associative groups such as polyvinyl alcohol,poly(meth)acrylamide, poly(meth)acrylic acid, polyvinylpyrrolidone,styrene/maleic anhydride or ethylene/maleic anhydride copolymers andtheir derivatives or also hydrophobically modified ethoxylatedpolyurethanes or polyacrylates. In addition, anti-sedimentation agents,flow control agents, light stabilisers, catalysts, antifoaming agentssuch as, for example, silicone-containing compounds; wetting agents andadhesion-promoting substances may be used. Wetting agents are alsounderstood to include known paste resins which may be used for betterdispersion and milling of the pigments.

The proportion of solvents in aqueous coating agents according to theinvention is preferably less than 20 wt. %, particularly preferably lessthan 15 wt. %, very particularly preferably less than 10 wt. %. Theseare conventional lacquer solvents and may arise from preparation of thebinder or may be added separately. Examples of such solvents aremonohydric or polyhydric alcohols, e.g. propanol, butanol, hexanol;glycol ethers or esters, e.g. diethylene glycol dialkyl ethers,dipropylene glycol dialkyl ethers, each with C1-C6 alkyl groups,ethoxypropanol, butyl glycol; glycols, e.g. ethylene glycol, propyleneglycol and its oligomers, N-alkylpyrrolidones such as e.g.N-methylpyrrolidone and ketones such as methyl ethyl ketone, acetone,cyclohexanone; aromatic or aliphatic hydrocarbons, e.g. toluene, xyleneor linear or branched aliphatic C6-C12 hydrocarbons. Aqueous coatingagents according to the invention may contain one or more inorganicand/or organic colour and/or effect-providing pigments and optionallyalso at least one filler.

Examples of effect-providing pigments are metal pigments, e.g.consisting of aluminium, copper or other metals; interference pigmentssuch as e.g. metal oxide coated metal pigments, e.g. titanium dioxidecoated aluminium, coated mica such as e.g. titanium dioxide coated micaand graphite effect pigments. Examples of colour-providing pigments andfillers are titanium dioxide, micronised titanium dioxide, iron oxidepigments, carbon black, silicon dioxide, barium sulfate, micronisedmica, talcum, kaolin, chalk, azo pigments, phthalocyanine pigments,quinacridone pigments, pyrrolopyrrol pigments, perylene pigments.

The effect pigments are generally provided in the form of a commerciallyavailable aqueous or non-aqueous paste; preferably water-dilutable,organic solvents and additives are optionally added and then they aremixed with the aqueous binder under shear. Powdered effect pigments mayfirst be processed with preferably water-dilutable organic solvents andadditives to give a paste.

Coloured pigments and/or fillers may, for example, be rubbed into someof the aqueous binder. The rubbing in process may also take place in aspecial water-dilutable paste resin. An example of a paste resin basedon polyurethane which can preferably be used in aqueous coating agentsaccording to the invention can be found in DE-A-40 00 889. Rubbing inmay be performed in conventional equipment which is familiar to a personskilled in the art. Then, the remaining proportion of aqueous binder oraqueous paste resin is used to complete the final rubbing in of thecoloured pigment.

If paste resins are present in aqueous coating agents according to theinvention, then these are added to the binder plus optionally presentcross-linking agents when calculating the resin solids.

Aqueous coating agents according to the invention contain bases asneutralising agents, for example the same neutralising agents as werementioned previously for use with the hybrid binder.

Aqueous coating agents according to the invention are preferablyformulated as water-based base-coat lacquers such as are used formulti-layered finishes and are overpainted with transparent clearlacquers. These types of water-based base-coat lacquers have a solidscontent of, for example, 10-50 wt. %; for effect water-based base-coatlacquers it is preferably, for example, 15-30 wt. %, for monocolouredwater-based base-coat lacquers it is preferably higher, for example20-45 wt. %. The ratio by weight of pigment (including filler) to binderplus optional cross-linking agent plus optional paste resin inwater-based base-coat lacquers is, for example, between 0.03:1 and 3:1;for effect water-based base-coat lacquers it is preferably 0.06:1 to0.6:1, for monocoloured water-based base-coat lacquers it is preferablyhigher, for example 0.06:1 to 2.5:1, each with respect to the weight ofsolids.

Water-based base-coat lacquers according to the invention may be appliedby conventional methods. They are preferably applied by spraying to givea dry layer thickness of 8 to 50 μm; for effect water-based base-coatlacquers the dry layer thickness is preferably, for example, 10 to 25μm, for monocoloured water-based base-coat lacquers it is preferablyhigher, for example 10 to 40 μm. Application may also be performed togive very thick layers, for example 25 to 50 μm, in one spray passbecause the aqueous coating agents according to the invention have ahigh sagging limit. Multiple spray processes and the associatedintermediate drying procedures or intermediate evaporation procedurescan be avoided. Application preferably takes place as a wet-on-wetprocess, i.e. after an evaporation phase, e.g. at 20 to 80° C., thewater-based base-coat lacquer layers are overpainted with a conventionalclear lacquer in a dry layer thickness of preferably 30 to 60 μm anddried or cross-linked in common with this at temperatures of, forexample, 20 to 150° C. The drying conditions for the topcoat layer(water-based base-coat lacquer according to the invention and clearlacquer) are governed by the clear lacquer system used. For repairpurposes, temperatures of, for example, 20 to 80° C. are preferred. Forthe purposes of mass-production lacquering, temperatures of more than100° C., for example more than 110° C., are preferred.

In principle, any known clear lacquers or transparent pigmented coatingagents are suitable as the clear lacquer. Here, eithersolvent-containing, single-component or two-component clear lacquers,water dilutable clear lacquers, powder coating clear lacquers, aqueouspowder coating clear lacquer slurries or clear lacquers which can becured by irradiation may be used.

Multi-layered finishes produced in this way may be applied to a widevariety of substrates. In general, they are metallic or plasticssubstrates. These are frequently pre-coated, i.e. plastics substratesmay be provided with e.g. a plastics primer, metallic substratesgenerally have an electrophoretically applied primer and optionally alsoone or more further lacquer layers such as e.g. a filler layer. Theselayers have generally been cured.

Multi-layered finishes obtained with water-based base-coat lacquersaccording to the invention satisfy the currently conventionalrequirements for motor vehicle finishes. Water-based base-coat lacquersaccording to the invention are thus suitable for initial vehiclefinishes and for vehicle repair finishes, but they may also be used inother areas, e.g. plastics finishes, in particular for finishes onvehicle parts.

The invention also provides a substrate, coated with a multi-layeredcoating which has been obtained by applying at least one primer,preferably based on a water-dilutable coating agent, applying a colourand/or effect-providing base-coat lacquer layer using an aqueous coatingagent according to the invention, optionally drying the base-coatlacquer layer and applying a transparent coating agent as a top layerand then heating the coated substrate. Optionally, further additionallayers may be added to this multi-layered finish.

Aqueous coating agents according to the invention are suitable inparticular as water-based base-coat lacquers for producing a colourand/or effect-providing coating layer within a multi-layered finish.Aqueous coating agents according to the invention may be applied in onlyone spray pass, even when producing a thick layer, which is ofparticular importance when applying layers of lacquer with poorlycovering shades of colour.

EXAMPLES Preparation Example 1

145.4 g of a polyester of adipic acid, neopentyl glycol and isophthalicacid (OH value: 109 mg KOH/g) and 8.0 g of dimethylolpropionic acid aredissolved in 69.6 g of N-methylpyrrolidone and heated to 40° C. Then,55.8 g of isophorone diisocyanate are added in such a manner that areaction temperature of 80° C. is not exceeded. This is maintained untilan NCO content of 2% (with respect to solid resin and determinedaccording to DIN 53185) is achieved. Then 7.0 g of3-aminopropyltriethoxysilane and 15.0 g of dodecanol are added, oneafter the other. The reaction mixture is held at 80° C. until free NCOgroups can no longer be detected (titration). Then 128.0 g of methylmethacrylate are added. 5.4 g of triethylamine and 5.4 g of deionisedwater are added and thoroughly incorporated. After adding 864.0 g ofdeionised water, a finely divided aqueous dispersion is obtained. Now,250.0 g of butyl acrylate, 125.0 g of tert.-butyl acrylate and asolution of 62.0 g of deionised water and 2.0 g of ammoniumperoxydisulfate are added continuously over the course of 2 h at 80° C.Finally, the mixture is maintained at 80° C. for 3 hours and adjusted toa solids content (60′ 150° C.) of 40.0 wt. % with deionised water.

Preparation Example 2

339.0 g of a polyester of adipic acid, neopentyl glycol andcyclohexanedicarboxylic acid (OH value: 104 mg KOH/g) and 13.7 g ofdimethylolpropionic acid are dissolved in 160.0 g of N-methylpyrrolidoneand heated to 40° C. Then, 125.0 g of isophorone diisocyanate are addedin such a manner that a reaction temperature of 80° C. is not exceeded.This is maintained until an NCO content of 2% (with respect to solidresin and determined according to DIN 53185) is achieved. Then 43.8 g of3-aminopropyltriethoxysilane and 20.8 g of diethanolamine are added, oneafter the other. The reaction mixture is held at 80° C. until free NCOgroups can no longer be detected (titration). Then 128.0 g of methylmethacrylate are added. 9.2 g of triethylamine and 9.2 g of deionisedwater are added and thoroughly incorporated. After adding 1300.0 g ofdeionised water, a finely divided aqueous dispersion is obtained. Now,240.0 g of butyl acrylate, 175.0 g of tert.-butyl acrylate and asolution of 100.0 g of deionised water and 4.0 g of ammoniumperoxydisulfate are added continuously over the course of 2 h at 80° C.Finally, the mixture is maintained at 80° C. for 3 hours and adjusted toa solids content (60′ 150° C.) of 40.0 wt. % with deionised water.

Preparation Example 3

772.0 g of a polyester of adipic acid, neopentyl glycol and isophthalicacid (OH value: 100 mg KOH/g) and 89.0 g of dimethylolpropionic acid aredissolved in 412.0 g of N-methylpyrrolidone and heated to 40° C. Then,375.0 g of isophorone diisocyanate are added in such a manner that areaction temperature of 80° C. is not exceeded. This is maintained untilan NCO content of 2% (with respect to solid resin and determinedaccording to DIN 53185) is achieved. Then 41.0 g of3-aminopropyltriethoxysilane and 89.2 g of dodecanol are added, oneafter the other. The reaction mixture is held at 80° C. until free NCOgroups can no longer be detected (titration). Then 886.0 g of styreneare added. 60.0 g of triethylamine are added and thoroughlyincorporated. After adding 4500.0 g of deionised water, a finely dividedaqueous dispersion is obtained. Now, 178.0 g of hydroxyethylmethacrylate, 712.0 g of butyl acrylate, 890.0 g of tert.-butyl acrylateand a solution of 850.0 g of deionised water and 50.0 g of ammoniumperoxydisulfate are added continuously over the course of 2 h at 80° C.Finally, the mixture is maintained at 80° C. for 3 hours and adjusted toa solids content (60═ 150° C.) of 40.0 wt. % with deionised water.

Preparation Example 4

697.3 g of a polyester of adipic acid, neopentyl glycol and isophthalicacid (OH value: 100 mg KOH/g) and 80.0 g of dimethylolpropionic acid aredissolved in 372.0 g of N-methylpyrrolidone and heated to 40° C. Then,338.0 g of isophorone diisocyanate are added in such a manner that areaction temperature of 80° C. is not exceeded. This is maintained untilan NCO content of 2% (with respect to solid resin and determinedaccording to DIN 53185) is achieved. Then 37.2 g of3-aminopropyltriethoxysilane and 83.6 g of dodecanol are added, oneafter the other. The reaction mixture is held at 80° C. until free NCOgroups can no longer be detected (titration). Then 400.0 g of methylmethacrylate are added. 54.2 g of triethylamine and 54.2 g of deionisedwater are added and thoroughly incorporated. After adding 3900.0 g ofdeionised water, a finely divided aqueous dispersion is obtained. Now,267.0 g of hydroxyethyl methacrylate, 1066.0 g of butyl acrylate, 663.0g of tert.-butyl acrylate and a solution of 1000.0 g of deionised waterand 40.0 g of ammonium peroxydisulfate are added continuously over thecourse of 2 h at 80° C. Finally, the mixture is maintained at 80° C. for3 hours and adjusted to a solids content (60′ 150° C.) of 40.0 wt. %with deionised water.

Lacquer Example 1

1.1 Preparing a Monocoloured, Red, Water-based Base-coat Lacquer

300 g of a conventional paste resin (in accordance with the example fromDE-OS 4 000 889) are blended with 350 g of a commercially available vatpigment (Colour index Red 168). The mixture is adjusted to a pH of 8.5with dimethylethanolamine and to a solids content of 50 wt. % by addingdeionised water. Then the mixture is dispersed in a pearl mill until itis transparent.

1.2

1.4 g of a commercially available thickener based on polyacrylic acid(solids: 10 wt. %, pH 7.5) are mixed with 129 g of the dispersion frompreparation example 1 and 40 g of the paste resin from example 1.1.Then, with stirring, 24 g of a commercially available, water-insoluble,melamine resin (Setamine US 138/BB 70 from the AKZO Co.) are added, withstirring. Finally, 10 g of the red paste from example 1.1 are added andstirred in until the mixture is homogeneous. The mix is adjusted toapplication viscosity with deionised water.

1.3 Applying the Water-based Base-coat Lacquer and a Clear Lacquer

The water-based base-coat lacquer obtained is applied, to give a drylayer thickness of 30 μm, by spraying onto a conventional, phosphatedcar body sheet which has been precoated with a cathodicelectrodeposition layer and with a filler. After application, the layeris allowed to evaporate at room temperature for 10 minutes and is thenpredried at 80° C. for 10 minutes. Finally, a commercially available,melamine resin curing car mass production lacquer based on an acrylateresin is overpainted in a dry layer thickness of 35 μm and dried at 120°C. (object temperature) for 18 minutes.

A multi-layered finish is obtained which complies with thespecifications which are becoming conventional for mass-produced carfinishes.

Furthermore, the water-based base-coat lacquer obtained is applied to aconventional, phosphated car body sheet which has been precoated with acathodic electrodeposition layer and with a filler, by spraying in awedge (dry layer thickness of 0 to 50 μm). This took place using alacquering robot without intermediate evaporation. The sagging limit was42 μm.

Lacquer Example 2

Lacquer example 1 was repeated with the difference that, instead of thedispersion from preparation example 1, the dispersion from preparationexample 2 is used. No sagging was observed, i.e. the sagging limit wasmore than 50 μm.

Lacquer Example 3

Preparing a Silver Metallic Two-layered Finish

20 g of a commercially available aluminium paste suitable for awater-based base-coat lacquer, with 65 wt. % of aluminium, 20 g of butylglycol, 6 g of N-methylpyrrolidone and 1 g of a commercially availablewetting agent are mixed with each other to give a bronze product. Then,1.4 g of a commercially based thickener based on polyacrylic acid(solids: 10 wt. %, pH 7.5) are added thereto. Then 129 g of thedispersion from preparation example 1 and 40 g of the paste resin fromlacquer example 1.1 are stirred into the bronze product. Finally, withstirring, 24 g of a commercially available, water-insoluble, melamineresin (Setamine US 138/BB 70 from the Akzo Co.) are added with stirring.The mixture is adjusted to application viscosity with deionised water.

The water-based base-coat lacquer obtained is applied by spraying onto aconventional, phosphated car body sheet which has been precoated with acathodic electrodeposition layer and with a filler. This was performedin such a way as to provide a dry layer thickness of 15 μm. Afterapplication, the lacquer is allowed to evaporate at room temperature for10 minutes and then predried at 80° C. for 10 minutes. Then acommercially available melamine resin curing car mass-production clearlacquer based on an acrylate resin is overpainted in a dry layerthickness of 35 μm and dried at 120° C. (object temperature) for 18minutes.

A multi-layered finish is obtained which complies with thespecifications which are becoming conventional for mass-produced carfinishes.

Furthermore, the water-based base-coat lacquer obtained is applied to aconventional, phosphated car body sheet which has been precoated with acathodic electrodeposition layer and with a filler, by spraying in awedge (dry layer thickness of 0 to 50 μm). This took place using alacquering robot without intermediate evaporation. The sagging limit is33 μm.

Lacquer Example 4

Lacquer example 3 is repeated with the difference that the dispersionfrom preparation example 2 is used instead of the dispersion frompreparation example 1. The sagging limit is 47 μm.

What is claimed is:
 1. An aqueous coating agent comprising an aqueousbinder dispersion and optionally organic solvents, cross-linking agents,pigments, fillers, conventional lacquer additives and additionalbinders, wherein the aqueous binder dispersion consists of apolyurethane/polymer hybrid polymer, wherein said hybrid polymer (a) hasa ratio by weight of polyurethane fraction to polymer fraction of 0.1:1to 50:1, (b) a hydroxyl value of 0 to 150 mg KOH/g, with respect to thesolid resin but excluding hydroxyl groups bonded to silicon, (c) an acidvalue of 1.5 to 60 mg KOH/g, with respect to the solid resin, (d) aconcentration of 0.5 to 300 mmol of silicon per 100 g of solid resin andassociated with the polyurethane fraction of the hybrid polymer andconsisting of siloxane bridges of the formula incorporated into thepolyurethane fraction, wherein said silicon concentration is obtained bypolymerization of olefinic unsaturated monomers in the presence ofpolyurethane resins; said polyurethane resins do not contain olefinicdouble bonds and do contain silicon in the form of siloxane bridges ofthe formula —Si—O—Si—.
 2. A process for preparing aqueous coating agentsaccording to claim 1, by preparing an aqueous binder dispersion andoptionally blending this with the required other components, as definedin claim 1, wherein the aqueous binder dispersion is prepared byconverting a polyurethane prepolymer which contains acid groups and doesnot contain olefinic double bonds, which has, on average, 0.7 to 9 R′—Ogroups bonded to silicon per molecule, in which R′=C1 to C8 alkyl orC(O)R′″, and R′″=C1 to C10 alkyl wherein the polyurethane prepolymer isoptionally dissolved in a solvent which is inert toward isocyanate andthe acid groups have optionally been previously neutralized, by addingwater and then subjecting the prepolymer to radical polmerizationtogether with one or more olefinancially unsaturated monomers.
 3. Aprocess according to claim 2, wherein the polyurethane prepolymers areprepared by reacting the free isocyanate groups in a polyurethaneprepolymer which does not contain double bonds a1) with one or morecompounds of the general formula((H—X—)_(n)R)_(a)Si(OR′)_(b)(R″)_(c)  (1)  where X═O, S, NH or NR^(iv),preferably NH or NR^(iv), R=a bifunctional, trifunctional ortetrafunctional, preferably bifunctional, organic group with a molecularweight of 13 to 500, R′=C1 to C8 alkyl or C(O)R′″, R″=R′″=C1 to C10alkyl, wherein R″ and R′″ may be identical or different, R^(iv)=C1 to C8alkyl, a=1, 2 or 3, b=1, 2 or 3, c=0, 1 or 2, n=1 to 3, wherein severalgroups R′, R″ and R′″ are identical or different and in which the sum ofa plus b plus c is four, a2) optionally with alkanolamines which containone or more NH₂ and/or NH groups and have an OH-functionality of atleast 1, and a3) optionally with one or more aliphatic C4-C36 alcoholsand/or amines.
 4. A process for preparing multi-layered finishes byapplying a base-coat lacquer layer and a clear lacquer layer to anoptionally pretreated substrate, wherein the base-coat lacquer layer isproduced by using a coating agent according to claim
 1. 5. A processaccording to claim 4, wherein the base-coat lacquer layer is applied toform a dry layer having a thickness of 8 to 50 μm.
 6. A processaccording to claim 4, wherein the base-coat lacquer layer is appliedusing a single spray process.
 7. A substrate coating with amulti-layered finish wherein at least one layer of the finish is thecoating agent of claim
 1. 8. The aqueous coating agent of claim 1 inwhich the polyurethane resins has on average 0.7 to 9 R′—O groups bondedto silicon per molecule in which R′=C1 to C8 alkyl or C(O)R′″, andR′″=C1 to C10 alkyl.